This invention relates to photographic apparatus of the self-developing type.
More particularly, the invention relates to an improved pressure roller used in such apparatus, and to a method of making such roller.
Such photographic self-developing apparatus uses film packs containing a (usually rectangular) film area to be developed and a processing fluid supply. The pack is advanced through a nip defined between two pressure rollers for spreading the processing fluid over the rectangular film or developing area. One of the rollers may be provided with a jacket of elastic material.
One of the major problems of such self-developing systems resides in the distribution of the processing fluid. Typically, spreading of the fluid over the film area is not uniform, particularly, in marginal regions of this area. The presence of undeveloped portions, of course, makes the finished picture effectively worthless.
In an attempt to solve this problem it has been proposed to place the processing fluid in pouches between two superposed sheet elements of the film pack which are secured at their common opposite longitudinal edges by edge-binding brackets. Each bracket has portions which extend inwardly away from the respectively associated longitudinal edge and which thus overlie portions of the external surfaces of the sheet elements. This means that the marginal portions of the film pack have a greater thickness than those portions which are located intermediate the longitudinal edges.
When the film pack is advanced through the nip of the pressure rollers, a pressure is generated upon the sheet elements which squeezes the processing fluid from the pouches and causes it to spread over the exposure area. However, because of the greater thickness of the marginal portions, these portions of the sheet elements are so firmly pressed together that the fluid can not penetrate between them to the border regions of the exposure area, so that these regions will not be properly developed unless the pressure is relieved.
To afford this relief, circumferentially-extending grooves are provided on opposite ends of one of the pressure rollers which is provided with a deformable outer layer. These grooves provide the aforementioned relief function. However, the width and depth of these grooves are very critical for proper development of the border regions of the exposure area. The deformable layer typically has a thickness of about one-tenth of a millimeter, and the depth of the grooves is typically about one-hundredth of a millimeter. If the depth of a groove is too shallow, longitudinal strips of the exposure area remain undeveloped; if the depth of the groove is too deep (for example, if it is even one micron oversized), not enough processing fluid will be present to develop the trailing (as considered in the travel direction of the film pack) corner regions of the exposure area. The technical aspects associated with holding the mechanical tolerances of the grooves have proven to be extremely costly and very difficult to reliably achieve and maintain in practice.
The commonly assigned U.S. Pat. No. 4,017,879 granted to Peter Lermann et al -- the entire contents of which are hereby incorporated by reference -- has proposed to make the elastic jacket of the one pressure roller more readily deformable at those axially spaced locations where the thicker marginal portions of the film pack pass through the nip between the two pressure rollers, or to form the jacket with circumferential grooves at these locations.
This has, in fact, been found to offer the desired advantages. However, it has also been found that the proposed constructions should desirably be further improved, especially with respect to ease of manufacture.